Tinnitus and Us

Survey’s indicate about 5% of all American adults admit to experiencing tinnitus. I use that qualifier in my first sentence because many people do not admit to having unintentionally damaged their hearing; especially musicians and audio “professionals” (using the term very tightly tied to the monetary definition of “professional”). Using that conservative number, at least 16 million US citizens are hearing tones (and probably voices for a loony percentage of that group) that don’t exist in the acoustic world. There is a financial reason for not admitting to tinnitus for many people in music, so expecting honesty from a group that is incentivized to lie about hearing deficiencies is irrational. For example, a recording engineer who admits his hearing is damaged badly enough that silent moments in a mix are filled with a variety of unrelated tones needs a younger, more physically capable assistant to be useful.

A great description from Dr. Amy Sarow on NPR’s 1A program from a few days ago, “What’s happening for those with tinnitus, the brain is searching for sound. And if you have some degree of hearing loss, which is the case for 80 to 90% of those with tinnitus, the brain says ‘Humm, something isn’t right here.’ And so it starts to increase the spontaneous firing rate of the nerve [intended to receive a specific frequency content] and this hyperactivity creates the perception of sound where there isn’t any.” Something about that “spontaneous firing rate of the nerve” explanation really struck an audible note with me. [pun intended] For years, I used an Automatic Gain Control (AGC) electronic analogy to explain the noises we hear in tinnitus. That wasn’t wrong, but it wasn’t entirely accurate either. And it wasn’t even slightly as elegant as the biological explanation.

One of the problems with that analogy is that it implies that the tinnitus frequency is directly related to the note you are hearing. That isn’t always the case. That spontaneous firing rate is likely to be more of a mechanical value generated by resonances in the nerve than a tone-loss relationship. I used to believe that the tinnitus tones were the frequencies lost by the hearing damage and that is also only sort of true.

More importantly, though, it is absolutely useful to understand that the very narrow spectrum of sounds that a typical hearing test provides (see at left) don’t give you much of a picture of potential damage. For example, you might test in the “normal” range at 1000Hz, but be functionally deaf at 1100Hz. Noise-induced hearing damage can be that specific. That mitigates against the value of a traditional, low-tech audiologist’s office test, but it really makes the new over-the counter programmable hearing aids look like the ideal choice for anyone even moderately technical.